1. Field of the Invention
The present invention relates in general to a video camera, and more paticularly to a negative film shooting apparatus for a video camera which is suitable to shooting of a negative film.
2. Description of the Prior Art
For example, in a negative film which is obtained by photographing an object through a still camera, an obtained image has inverted colors and black and white as compared with a real image. Namely, the image of the negative film has complementary colors with respect to the colors of the real image. For this reason, the colors and black and white of the real image can be obtained by printing the negative film. In this connection, the negative film is used for the purpose of printing. In result, in the case where the negative film is shot by a general video camera, the image is obtained which has the complementary colors with respect to the colors of the real image. In this case, in order to obtain the image of the real colors from the negative film, the video camera must be provided with an additional apparatus for inverting the colors and black and white of the image obtained upon shooting the negative film.
Referring to FIG. 1, there is shown a block diagram of a conventional video camera with no negative film shooting function. As shown in this drawing, the conventional video camera comprises a signal processor 1 for obtaining a luminance signal Y and color difference signals R-Y and B-Y from an image signal inputted therein, and an encoder 2 for inputting the luminance signal Y and the color difference signal s R-Y and B-Y from the signal processor 1 and outputting a composite video signal CVS. Herein, the reference numeral R designates a red signal and the reference numeral B designates a blue signal.
Since the video camera mentioned above with reference to FIG. 1 has no separate apparatus for shooting the negative film, the image obtained upon shooting of the negative film has the complementary colors with respect to the colors of the real image.
Referring to FIG. 2, there is shown a block diagram of a conventional negative film shooting apparatus for a video camera having a function for inverting the colors of the image obtained upon shooting of the negative film such that the resultant image has the same colors as those of the real image. As shown in this figure, the conventional negative film shooting apparatus comprises a chrominance subcarrier oscillator 3 for oscillating a chrominance subcarrier, a first phase shifter 4 for shifting a phase of the chrominance subcarrier from the chrominance subcarrier oscillator 3 by 0.degree., a second phase shifter 5 for shifting the phase of the chrominance subcarrier from the chrominance subcarrier oscillator 3 by 180.degree., a third-phase shifter 6 for shifting the phase of the chrominance subcarrier from the chrominance subcarrier oscillator 3 by 90.degree., a fourth phase shifter 7 for shifting the phase of the chrominance subcarrier from the chrominance subcarrier oscillator 3 by 270.degree., a signal processor 8 for obtaining color difference signals R-Y and B-Y from an image signal inputted therein, first and second switches 9 and 10 for transferring the chrominance carrier from the chrominance carrier oscillator 3 to the first and third phase shifters 4 and 6 upon shooting of a general object and to the second and fourth phase shifters 5 and 7 upon shooting of the negative film, respectively, according to a user's selection, a first modulator 11 for modulating the color difference signal R-Y from the signal processor 8 in response to an output signal from the first phase shifter 4 or an output signal from the second phase shifter 5, a second modulator 12 for modulating the color difference signal B-Y from the signal processor 8 in response to an output signal from the third phase shifter 6 or an output signal from the fourth phase shifter 7, and a mixer 13 for mixing output signals from the first and second modulators 11 and 12 and outputting the mixed signal as a carrier chrominance signal.
In accordance with the conventional video camera of the construction mentioned above with reference to FIG. 2, the obtained color difference signals R-Y and B-Y are modulated by the chrominance subcarriers of the phase differences of 0.degree. and 90.degree. upon shooting of the general object and by the chrominance subcarriers of the phase differences of 180.degree. and 270.degree. upon shooting of the negative film, respectively. The color inverting effect can be obtained from the construction of FIG. 2 in which the obtained color difference signals R-Y and B-Y are modulated by the chrominance subcarriers of the phase differences of desired angles. Therefore, the image of the shot negative film has the same colors as those of the real image. This construction is shown in Japanese Utility Model Laid-Open Publication NO. Sho. 62-119080, applied by Japanese International Communication Co., Ltd.
However, the conventional video camera with the above-mentioned construction has the following disadvantages:
First, since the conventional video camera is not provided with an apparatus for inverting the luminance signal corresponding to the black and white of the image, the real image cannot perfectly be obtained upon shooting of the negative film. Namely, the image of the shot negative film has the inverted luminance signal as well as the inverted color signal. For this reason, with only the apparatus for inverting the color signal as shown in FIG. 2, the real image cannot perfectly be obtained upon shooting of the negative film.
Second, the conventional video camera negative film shooting apparatus performs the color signal inversion with the chrominance subcarrier phase shifters, in which undesired time delay may occur. As a result, the phase shifters each must have such an accurate construction as to prevent the time delay. However, the accurate construction of the phase shifter results in a complexity thereof.